Brushless motor for hvac system

ABSTRACT

A brushless motor for a heating, ventilation, and air conditioning (HVAC) system. The brushless motor includes a rotor and a stator. The rotor has an odd number (X) of magnets. The stator defines an odd number (Y) of slots, each including a plurality of fractional-pitch phase windings. The brushless motor has a fundamental order that is (X·Y)/2, which is a non-integer number.

FIELD

The present disclosure relates to a brushless motor for a heating,ventilation, and air conditioning system.

BACKGROUND

This section provides background information related to the presentdisclosure, which is not necessarily prior art.

Brushless motors are commonly used for a variety of industrial andconsumer products, such as automotive related products, in particularblower motors for heating, ventilation, and air conditioning (HVAC)systems. Brushless motors have replaced conventional DC brush motors fora variety of reasons. One of the main reasons is to avoid and eliminatethe common excitation of brush noise that is induced due to contact andsliding of the brushes and commutator slots. The use of a brushlessmotor eliminates the brush noise, which is usually tonal (slot passingfrequency corresponding to the number of slots on the commutator), aswell as high frequency ticking/grinding noise.

Typical brushless motors have an odd number of magnets (m) and an evennumber of slots (s) on a stator and rotor or vice versa. As a result,current brushless motors can generate major magnetic harmonics at orderscorresponding to (m·s)/2, and minor sub-harmonics at multiples of m(e.g., if m=5 and n=10, major audible harmonics may be excited at(5·10)/2=25^(th) order of the rotational speed of the motor.

A brushless motor that suppresses this dominant harmonic would thereforebe desirable. The present disclosure advantageously provides for such abrushless motor, which has dominant harmonics at higher orders, whichare masked (inaudible) by the blower.

Current brushless motors experience dominant (audible) orders/tones atcertain rotational speeds, relatively low blower speeds when theair-rush noise that usually masks blower-induced noise is minimal. Themost dominant/audible tone (order) occurs at (m·n)/2 order. With currentbrushless motors, the product of (m·n) is an even number, and the orderoccurs at an integer number. This order gets further amplified whencoincident with HVAC system resonances. For example, for existingbrushless motors where m=4 and n=6, the dominant order is (4·6)/2=12.For current motors where m=8 and n=6, the dominant order is (8·6)/2=24.For current brushless motors where m=5 and n=6, the dominant order is(5·6)/2=15. Such dominant orders are undesirably audible because theyare not masked by the air-rush noise of the blower due to the relativelylow frequency and high energy of the orders. A brushless motor thatgenerates relatively high frequency orders with relatively less energywould therefore be desirable because such orders will be masked by thenoise of the blower and advantageously be inaudible.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

The present disclosure includes a brushless motor for a heating,ventilation, and air conditioning (HVAC) system. The brushless motorincludes a rotor and a stator. The rotor has an odd number (X) ofmagnets. The stator defines an odd number (Y) of slots, each including aplurality of fractional-pitch phase windings. The brushless motor has afundamental order that is (X·Y)/2, which is a non-integer number.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselect embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 illustrates an exemplary brushless motor in accordance with thepresent disclosure; and

FIG. 2 illustrates exemplary orders of brushless motors in accordancewith the present disclosure, as well as an exemplary order of a priorart brushless motor, relative to overall noise generated by an exemplaryblower.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

FIG. 1 illustrates an exemplary brushless motor in accordance with thepresent disclosure at reference numeral 10. The brushless motor 10 canbe used with any suitable device, such as a blower of a heating,ventilation, and air conditioning (HVAC) system, particularly a vehicleHVAC system. The brushless motor 10 generally includes a shaft 12, arotor 14, and a stator 16. The rotor 14 includes a plurality of magnets20. The stator 16 defines a plurality of slots 22. Each one of the slots22 includes fractional-pitch phase windings.

Unlike current brushless motors, the brushless motor 10 according to thepresent disclosure has an odd number (X) of magnets 20, and an oddnumber (Y) of slots 22. Existing brushless motors have an even number ofslots and odd number of magnets (or vice versa), which results in thegeneration of low frequency/high energy orders, which are undesirablyaudible, particularly at low blower speeds and sometimes at higherblower speeds. By having an odd number (X) of magnets 20 and an oddnumber (Y) of slots 22, the brushless motor 10 of the present disclosureadvantageously generates relatively higher dominant orders, which aregenerally inaudible, and/or readily masked by the high frequency airrush noise.

The brushless motor 10 can have any suitable number of magnets 20, suchas five magnets 20 or seven magnets 20. The motor 10 can also have anysuitable number of odd slots 22, such as 9, 11, 13, 15, or 27 slots 22.Table 1 below lists the fundamental orders for an exemplary rotor 14having five magnets 20, and 9, 11, 13, 15, or 27 slots 22. Table 1 alsolists the fundamental orders for an exemplary rotor 14 having sevenmagnets 20, and 9, 11, 13, 15, or 27 slots 22. Stators with 9, 15, 21,27, 33 and so on . . . slots advantageously can be mechanically balancedin three phases.

The fundamental order is calculated based on: (X*Y)/2. As set forth inTable 1, each one of the fundamental orders of the brushless motor 10 isa non-integer. Thus the corresponding dominant order, which is twice thefundamental order, is higher than the dominant orders of currentbrushless motors having an even number of slots or magnets. Therelatively higher dominant orders of the motor 10 have a higherfrequency and less energy as compared to orders of current brushlessmotors. As a result, the dominant orders of the motor 10 are higher andadvantageously inaudible.

TABLE 1 NO. NO. OF ROTOR OF STATOR FUNDAMENTAL DOMINANT MAGNETS (X)SLOTS (Y) ORDER (X · Y)/2 ORDER 5 9 22.5^(th) 45^(th) 5 11 27.5^(th)55^(th) 5 13 32.5^(th) 65^(th) 5 15 37.5^(th) 75^(th) 5 27 67.5^(th)135^(th)  7 9 31.5^(th) 63^(rd) 7 11 38.5^(th) 77^(th) 7 13 45.5^(th)91^(st) 7 15 52.5^(th) 105^(th)  7 27 94.5^(th) 189^(th) 

FIG. 2 illustrates the amount of noise generated by a typical vehicleHVAC blower at various speeds at line A. A 30^(th) order generated by acurrent brushless motor with 5 magnets and 12 stator slots at variousmotor speeds is illustrated at reference letter B. At low speeds, suchas at about 1600 rpm, the 30^(th) order of the exemplary existingbrushless motor is only about 10 dB (or less) lower than the overalldecibel level A of the exemplary blower motor. This is undesirablebecause typically such a difference of 10 dB is not significant enoughfor the 30^(th) order B of the existing brushless motor to be masked bythe overall noise generated by the blower represented by line A. The30^(th) order at line B is audible generally because the 30^(th) order Bhas a low frequency and high energy.

Line C of FIG. 2 illustrates an exemplary 55^(th) order generated by abrushless motor 10 according to the present disclosure having a rotor 14with an odd number (X) of magnets 20 equal to 5, and a stator 16defining an odd number (Y) of slots 22 equal to 11, which results in a27.5^(th) fundamental order and a 55^(th) dominant order. Line D of FIG.2 illustrates an exemplary 65^(th) order of a brushless motor 10according to the present disclosure having a rotor 14 with an odd number(X) of magnets 20 equal to 5, and a stator 16 defining an odd number (Y)of slots 22 equal to 13. Lines E and F of FIG. 2 illustrate an exemplary45th order and an exemplary 75th order respectively of brushless motors10 according to the present disclosure having a rotor 14 with an oddnumber (X) of magnets 20, and a stator 16 defining an odd number (Y) ofslots 22.

The delta between the overall decibel level A and the 30th order at lineB is a minimum, thus the 30th order dominates and contributes most tothe overall dBA at line A. Whereas with all the higher orders generatedby using a combination of odd number of slots and odd number of magnetsin accordance with the present disclosure, the delta dBA is larger, andhence only slightly audible and not annoying. In addition, it willeasily get masked by the higher air-rush noise at higher blower RPMsunlike the 30th order, which is enhanced due to its generation at 1,600RPM and its coincidence with any of the HVAC system resonances, such asbut not limited to an 800 Hz HVAC system resonance.

As illustrated in FIG. 2, the 55^(th) order at line C, the 65^(th) orderat line D, the 45^(th) order at line E, and the 75^(th) order at line F,have a relatively higher frequency, and less energy, as compared to the30^(th) order B. Thus the difference between the overall noise level ofthe exemplary blower at line A and each of the 55^(th) order at line C,the 65^(th) order at line D, the 45^(th) order at line E, and the75^(th) order at line F is far greater than 10 dB, such as about 30 dB.The 55^(th), 65^(th), 45^(th), and 75^(th) orders generated by theexemplary brushless motors 10 according to the present disclosure aregenerally masked by the overall sound generated by the blower (line A),thus making the orders of the brushless motor 10 advantageouslyinaudible or less annoying. FIG. 2 thus illustrates the difference infrequency and amplitude between the 30^(th) order of the exemplaryexisting brushless motor and each of the 55^(th), 65^(th), 45^(th) and75^(th) orders of the brushless motor 10 according to the presentdisclosure. FIG. 2 shows that the 30^(th) order has a lower frequencyand amplitude as compared to the 55^(th), 65^(th), 45^(th), and 75^(th)orders. In addition, the 30^(th) order readily coincides with the HVACsystem resonances at lower frequencies, making it louder.

The present teachings thus advantageously provide for a brushless motor10 having a rotor 14 with an odd number (X) of magnets 20, and a stator16 defining an odd number (Y) of slots 22. The motor 10 has afundamental order that is equal to (X·Y)/2, which is a non-integernumber. As a result, the corresponding dominant order will be higherthan the dominant orders of existing brushless motors with an evennumber of slots. The higher dominant orders of the brushless motors 10according to the present disclosure are advantageously inaudible becausethe higher dominant orders have a relatively higher frequency than, andrelatively lower energy than, existing brushless motors having an evennumber of slots. Noise generated by the brushless motor 10 is thusadvantageously masked by the overall noise generated by the associatedblower. The high frequency orders of the brushless motors 10 inaccordance with the present disclosure have relatively less energy ascompared to existing brushless motors, thus making the brushless motors10 of the present disclosure advantageously quieter.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

What is claimed is:
 1. A brushless motor for a heating, ventilation, andair conditioning (HVAC) system, the brushless motor comprising: a rotorhaving an odd number (X) of magnets; and a stator defining an odd number(Y) of slots each including a plurality of fractional-pitch phasewindings; wherein the brushless motor has a fundamental order that is(X·Y)/2, which is a non-integer number.
 2. The brushless motor of claim1, wherein the rotor has 5 magnets.
 3. The brushless motor of claim 2,wherein the stator has 9 slots, the fundamental order is [(5·9)/2]22.5th, and the dominant order is 45th order.
 4. The brushless motor ofclaim 2, wherein the stator has 11 slots, the fundamental order is[(5·11)/2] 27.5th, and the dominant order is 55th order.
 5. Thebrushless motor of claim 2, wherein the stator has 13 slots, thefundamental order is [(5·13)/2] 32.5th, and the fundamental frequency is65th order.
 6. The brushless motor of claim 2, wherein the stator has 15slots, the fundamental order is [(5·15)/2] 37.5th, and the fundamentalfrequency is 75th order.
 7. The brushless motor of claim 2, wherein thestator has 27 slots, the fundamental order is [(5·27)/2] 67.5th, and thefundamental frequency is 135th order.
 8. The brushless motor of claim 1,wherein the rotor has 7 magnets.
 9. The brushless motor of claim 8,wherein the stator has 9 slots, the fundamental order is [(7·9)/2]31.5th, and the fundamental frequency is 63rd order.
 10. The brushlessmotor of claim 8, wherein the stator has 11 slots, the fundamental orderis [(7·11)/2] 38.5th, and the fundamental frequency is 77th order. 11.The brushless motor of claim 8, wherein the stator has 13 slots, thefundamental order is [(7·13)/2] 45.5th, and the fundamental frequency is91st order.
 12. The brushless motor of claim 8, wherein the stator has15 slots, the fundamental order is [(7·15)/2] 52.5th, and thefundamental frequency is 105th order.
 13. The brushless motor of claim8, wherein the stator has 27 slots, the fundamental order is [(7·27)/2]94.5th, and the fundamental frequency is 189th order.
 14. The brushlessmotor of claim 1, wherein half the product of the odd number of magnetsand the odd number of slots is a non-integer.
 15. The brushless motor ofclaim 1, wherein the fundamental order is a lowest integer frequency ofa harmonic order.
 16. The brushless motor of claim 1, wherein thefundamental order is a first harmonic of an integer number.
 17. Thebrushless motor of claim 1, further comprising the HVAC system includingthe brushless motor.
 18. A heating, ventilation, and air conditioning(HVAC) system comprising: a brushless motor; a rotor of the brushlessmotor having an odd number (X) of magnets; and a stator of the brushlessmotor defining an odd number (Y) of slots each including a plurality offractional-pitch phase windings; wherein the brushless motor has afundamental order that is (X·Y)/2, which is a non-integer number; andwherein the fundamental order is a lowest integer frequency of aharmonic order.
 19. The HVAC system of claim 18, wherein the rotor has 5magnets or 7 magnets.
 20. The HVAC system of claim 18, wherein thestator has 9, 11, 13, 15, or 27 slots.